Projections by the Energy Information Agency and current Intergovernmental Panel on Climate Change (IPCC) expect worldwide electric power demand to double from its current level of about 2 terawatts electrical power (TWe) to 4 TWe by 2030, possibly reaching 8-10 TWe by 2100. They also expect that for the next 30 to 50 years, the bulk of the demand of electricity production will be provided by fossil fuels, typically coal and natural gas. Coal supplies 41% of the world's electric energy today, and is expected to supply 45% by 2030. In addition, the most recent report from the IPCC has placed the likelihood that man-made sources of CO2 emissions into the atmosphere are having a significant effect on the climate of planet earth at 90%. “Business as usual” baseline scenarios show that CO2 emissions could be almost two and a half times the current level by 2050. More than ever before, new technologies and alternative sources of energy are essential to meet the increasing energy demand in both the developed and the developing worlds, while attempting to stabilize and reduce the concentration of CO2 in the atmosphere and mitigate the concomitant climate change.
Nuclear energy, a non-carbon emitting energy source, has been a key component of the world's energy production since the 1950's, and accounts for about 16% of the world's electricity production, a fraction that could—in principle—be increased. Several factors, however, make its long-term sustainability difficult. These concerns include the risk of proliferation of nuclear materials and technologies resulting from the nuclear fuel cycle; the generation of long-lived radioactive nuclear waste requiring burial in deep geological repositories; the current reliance on the once through open nuclear fuel cycle; and the availability of low cost, low carbon footprint uranium ore. In the United States alone, nuclear reactors have already generated more than 55,000 metric tons (MT) of spent nuclear fuel (SNF). In the near future, the US will have enough spent nuclear fuel to fill the Yucca Mountain geological waste repository to its legislated limit of 70,000 MT.
Fusion is an attractive energy option for future power generation, with two main approaches to fusion power plants now being developed. In a first approach, Inertial Confinement Fusion (ICF) uses lasers, heavy ion beams, shock ignition, impulse ignition, pulsed power or other techniques to rapidly compress capsules containing a mixture of isotopes of hydrogen, typically, deuterium (D) and tritium (T). As the capsule radius decreases and the DT gas density and temperature increase, DT fusion reactions are initiated in a small spot in the center of the compressed capsule. These DT fusion reactions generate both alpha particles and 14.1 MeV neutrons. A fusion burn front propagates from the spot, generating significant energy gain. A second approach, Magnetic Fusion Energy (MFE) uses powerful magnetic fields to confine a DT plasma and to generate the conditions required to sustain a burning plasma and generate energy gain.
Important technology for inertial confinement fusion is being developed primarily at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in Livermore, Calif. At LLNL a laser-based inertial confinement fusion project designed to achieve thermonuclear fusion ignition and burn utilizes laser energies of 1 to 1.3 MJ. Fusion yields of the order of 10 to 20 MJ are expected. Fusion yields in excess of 200 MJ could be expected to be required in central hot spot fusion geometry if fusion technology, by itself, were to be used for cost effective power generation. Thus, significant technical challenges remain to achieve an economy powered by pure inertial confinement fusion energy.
In the 1950's, Andrei Sakharov discussed the idea of fusion-fission engines in which a fusion reaction generates neutrons for a fission engine. Hans Bethe and Nikolai Basov expanded on his ideas in the 1970's and 1980's, as did many other groups around the world. The focus of some of these studies was on the use of fusion neutrons to generate fuel for fast nuclear reactors, although Basov and others discussed the possibility of using laser-driven fusion targets to drive a fission blanket for generating commercial power. Many proposals have also been made to use accelerators to generate neutrons that can then be used to transmute nuclear waste and generate electricity. Fusion-fission engines, however, did not advance beyond a conceptual stage. For example, LLNL investigated conceptual concepts for ICF-based fusion-fission hybrids in the 1970's. See, for example, “US-USSR Symposium on Fusion-Fission Reactors,” Jul. 13-16, 1976, Hosted by Lawrence Livermore Laboratory. The current generation of enabling technology, including computational design tools, optical materials, diode-pumped solid state lasers, and high burn-up tristructural-isotropic (TRISO) fuels, however, are required to move the conceptual ideas toward realization. Similarly, accelerator based schemes have not advanced significantly, in part because a complete nuclear fuel cycle—including uranium enrichment and nuclear waste reprocessing—is still required to generate economical electricity. As a result the efficiency and cost of those systems is prohibitive relative to the benefit of transmuting nuclear waste.
Typical of additional early publications speculating upon a fusion-fission hybrid are articles: The Fusion Hybrid, by Hans A. Bethe in Physics Today 32(5), 44 (1979), Concept of a Coupled Blanket System for the Hybrid Fission-Fusion Reactor by A. P. Barzilov, A. V. Gulevich, A. V. Zrodnikov, O. F. Kukharchuk, V. B. Polevoy, Institute for Physics & Power Engineering, 1, Bondarenko Sq., Obninsk, Russia 249020 in Proc. Intern. Conf. SOFE'95, 1995, and the article, Hybrid Fission-Fusion Reactor Initiated by a Laser, by A. P. Barzilov, A. V. Gulevich, O. F. Kukharchuk and A. V. Zrodnikov, Institute of Physics & Power Engineering, Obninsk 249020 RUSSIA, Technical Physics Laboratory, Copyright©1997-2000, (http://www.ippe.obninsksuipodr/tpl/pub/html/1/ref1a.html).